To an extent you can. True, Google ads appear different for all viewers based on cookies and other algorithms, but you absolutely can tell Google what you do NOT want appearing on your site.
https://support.google.com/adsense/answer/164657

What I asked in my email to you, Jasmin, still stands.
Why not ask ethical labels to advertise on your site instead of google ads? That way everyone wins (you get some side income to keep the site going and the designers get to show off their wares).

We try to maintain a church-and-state separation between editorial and advertising; I'll forward your concerns, but if you want to talk to the advertising folks directly, you can email [email protected]

Hi Radcatalyst-
There aren't enough small ethical business advertisers out there to support the running of our website. We've been doing this for years, believe me we've tried. Google ads is the only sustainable revenue source to support the operations of this website. The irony of your comment is that if you're seeing a Forever 21 ad, it means you've been browsing the Forever 21 website. (Not saying you shop there but you've been looking at their website for some reason). Google ads are based on the cookies that viewers pick up from websites they visit.

Hi, Jill
Thanks for addressing this.
As for the Forever 21 ad, you're absolutely right that it came from my cookies as I was looking to see what kind of things people are wearing right now. But are you saying that BuffaloRach is wrong and that you can't control the type of Ads that Google shows (like fast fashion such as Gap, Walmart, and Forever 21)?

Hey Radcatalyst-
Buffalorach is right in that we can block ads from individual urls, so we could block gap.com and forever21.com We can discuss internally whether or not we can block those individual brands. Unfortunately, while we can block certain individual urls, since the majority of fashion brands out there are engaging in the third-world-labor "fast-fashion" thing, it would be impossible to block every garment brand that engages in developing country labor. But we'll try to block the most obvious and problematic brands, (ie the ones who won't sign the Bangladesh safety accord), such as Gap.

Yeah, I definitely understand that it's not just the big fashion brands that use sweatshop labor and that unless there is some sort of transparency, you're not sure how a garment or accessories are made. It bothers me that there isn't an international fair trade seal yet for clothing (but I understand the politics behind that, too) but yes, I believe blocking the big brands right now makes the most sense. Do you know if Target signed the pledge (since those are the predominant ads that are showing up for me right now on your Adchoices banner and side ad)?